Couplings for removably locking a hub axially on a shaft are well known. The hub may mount another shaft to which the removable connection is to be made or may mount, for example, the yoke of a universal joint.
Any application in which one member needs to be mounted co-axially and axially locked on a rotary power shaft may require such a coupling. For example, one common application of such a coupling is in connecting the power input shaft of an agricultural implement to the power takeoff shaft of a tractor. In this case, the hub typically mounts the yoke of a universal joint and is internally splined to match the external splines on the tractor's power take-off shaft, so as to establish a rotary power transmissive coupling between the hub and the power take-off shaft.
The hub is typically locked onto the shaft by locking members which are slidable in radially extending slots through the hub so as to engage a circumferential recess or raceway in the splined power take-off shaft of the tractor. A collar around the outside of the hub is biased into a locking position by a spring so as to prevent the locking members from backing out of the raceway in the shaft.
An example of such a coupling is disclosed in U.S. Pat. No. 4,900,181. In the coupling disclosed in this patent, a stop is formed in the collar which extends radially inwardly so that the collar can be tilted so that the stop comes to rest against another stop which is formed on the hub. When the locking elements are urged radially outwardly by engagement with the shaft when the shaft is inserted into the hub, the locking members center the collar so as to disengage the two stops and allow the collar to move into the locked position under the bias of a spring. However, when in the locked position, the collar can be moved therefrom to be locked in the disengaged position, even though the shaft is fully inserted in the hub, with the locking members engaged in the raceway. Thus, with this design, the coupling may appear to be in the locked position with the shaft fully inserted in the hub, when in fact the collar is locked in the disengaged position.